Heretofore, cooling of engine main shaft bearings has been done by lateral injection of oil or, utilizing centrifugal force, by means of cooling oil supplied below the shaft to be supported. The known outer-race cooling through a cooling channel in the outer race of the bearing cools the outer bearing race directly and contributes to a partial decoupling of the lubrication and cooling of bearings. Also known is a direct outer-race cooling which, in accordance with publication EP 2 304 259, takes place in the rigid bearing seat without additional squeeze film damping or, as described in publication WO 2011/067154, in a squeeze-film-damped seat with combined outer-race cooling and squeeze film damping. The combination of direct outer-race cooling and squeeze film damping can be accomplished with a stationary outer race or a rotating outer race, as described in publication DE 10 2012 203 933.
In addition, there are known rolling-element bearings with both a steel contact partner and a ceramic contact partner, where the steel contact partner has selectively introduced residual compressive stresses, as described in US 2012/0037278 A1.
The fatigue strength of the heretofore used heat-resistant steels decreases with increasing temperature. Furthermore, the oils used for lubrication and heat dissipation are limited in operating temperature, and thus, with the currently used bearing materials and oils, the temperature in the contact region cannot be significantly increased. The primary disadvantage is that the load on the outer race contacts is decisively negatively affected by the centrifugal forces of the steel rolling elements. With the heretofore used steel rolling elements, the centrifugal force is very high, especially at high rotational speeds, and requires higher cooling oil flow rates, which, in turn, are associated with increased bearing power losses and a larger-dimensioned oil system architecture, such as pumps, supply and discharge lines, seals, etc.